Lead frame for assembly for thin small outline plastic encapsulated packages

ABSTRACT

A lead frame for the assembly of thin small outline packages incorporating a semiconductor circuit is provided in a generally rectangular form including a plurality of conductive leads opposing one another about the longitudinal sides of the lead frame and a die mounting portion centered therebetween. In addition, a pair of leads is provided at the distal ends of the lead frame which are stamped in a general “S” shape. These stamped leads extend downwardly from the lead frame and are within the footprint of the lead frame. The footpads of these additional leads remain exposed as the lead frame is encapsulate in a plastic molded package and are level with the bottom of the molded package.

FIELD OF THE INVENTION

[0001] The present invention relates to semiconductor packaging ingeneral and, more particularly, to a lead frame assembly for increasingmetallic lead count in a thin small outline semiconductor package suchas TSOP, MSOP, and other micro-series packages.

BACKGROUND OF THE INVENTION

[0002] Small outline packaging is well known in the art of micro seriespackages. Typical of the art are the TSOP 5 and TSOP 8 packages. TheTSOP 5 package has a greater die-mounting pad than the TSOP 8 packagebut is only available with five external conductive leads. This limitsthe complexity and functionality of the semiconductor device that can beencapsulated within the package.

[0003] The TSOP 8 package can have eight isolated conductive leads foran 8 pin I/O count but has a restrictive die-mounting portion. Thissmaller die-mounting portion is typically too small to accommodate aneight pin semiconductor device. This packaging may result inhigher/bigger packaging and required packaging space.

[0004] Accordingly, a need exists for a small outline package, whichmaintains the larger die-mounting area such as the TSOP 5 micro-seriespackage while having superior lead count as available in the smalloutline micro-series package. In addition, the additional lead countshould not cause an increase in the minimal packaging outline.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is an enlarged plan view of the lead frame of the presentinvention;

[0006]FIG. 2 is a side view of the lead frame illustrating downwardextending leads of the present invention;

[0007]FIG. 3 is a side view of the encapsulated lead frame assembly andsemiconductor package; and

[0008]FIG. 4 illustrates a type of semiconductor circuit that may bemanufactured utilizing the additional leads of the lead frame of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

[0009] Turning now to FIG. 1 there is shown an expanded plan view of agenerally rectangular lead frame 10 in accordance with the presentinvention that, when incorporated into a semiconductor packagearrangement, provides additional leads for more complex circuitry in amicroseries package as will be more completely described. Lead frame 10includes a pair of die mounting portions or flags 12A and 12B connectedrespectively to metallic or conductive leads 14 and 16 that extendexternally to the molded plastic semiconductor package. In some cases anintegrated circuit die 11 (shown in dashed outline form) may be mountedto both flags 12A and 12B in which case only one of the leads 14 or 16is used. Additionally, lead frame 10 includes conductive metallic leads18, 20, 22, and 24 also extending externally from one side of theplastic encapsulation package as will be shown. The outline of theplastic semiconductor package, which encapsulates lead frame 10 andwithin which the semiconductor circuit die 11 resides, is shown at 30.Stamped lead frame 10 uses metallic tie bars 32, 34, 35, and 37 to addstability to the thin lead frame during assembly process. Additionalstrips 36 and 38 provide stability, as well as, manufacturability in atypical manner. Openings 40, 42, 44, and 46 formed in the strips 36 and38 are utilized in a known manner to position lead frames 10 in processequipment such that the strip is moved through an assembly machine.

[0010] Lead frame 10 as so far described above is fairly conventional instructure. In addition, the assembly process for bonding and connectingthe semiconductor circuit to the leads within the plastic encapsulationpackage referred to above is also known. The uniqueness of lead frame 10and the semiconductor package made up thereof is the inclusion ofadditional conductive leads 48 and 50 formed at both ends of theelongated direction of lead frame 10. As shown in FIG. 2 molded package30 encapsulates lead frame 10 and opposing leads 48 and 50. Leads 48 and50 are stamped during the manufacturing process in a general “S” shapeso that they are effectively locked to the package such that the bottomfoot pads 48A and 50A are essentially at the bottom level of package 30but are exposed to provide connection to internal semiconductorcircuitry.

[0011] Turning to FIG. 3 there is shown the final assembledsemiconductor package 30 in side view. The thickness of leads 48 and 50as well as the other leads and tie bars are exaggerated in this view forclarity. In reality, footpad's 48A and 50A are at the same level as thebottom of molded package 30 and lie within the external boundaries atopposing parallel and perpendicular ends thereof.

[0012] The aforedescribed novel lead frame enables a more complexintegrated circuit to be placed within the package than prior art thinsmall outline packages (TSOP). This is possible since a larger diemounting portion is made possible by the additional leads 48 and 50being placed at opposing longitudinal ends of lead frame 50. The “s”shape of these two leads allow the lead frame to fit within thefootprint of a TSOP while providing two additional leads. For example,referring to FIG. 4, a more complex circuit can be incorporated into theinventive lead frame package than previous TSOPs. Thus, in oneillustrative application, a dual operational amplifier circuit isprovided requiring eight leads.

[0013] In summary, what has been described is a novel lead frame for usein micro-series packages. The lead frame provides a die pad large enoughto accommodate larger and more complex semiconductor circuitry byincorporating a pair of additional leads. These leads are placed atopposite ends along the longitudinal sides of the generally rectangularlead frame. They are then stamped in a “S” shaped configuration toprovide effective locking in the package and to be exposed within thefoot print of the package and at the bottom level thereof. Thus, thelead frame, semiconductor package, provides the advantage of keepingwithin conventional TSOP dimensional guidelines while providing up totwo additional leads thereby allowing more complex circuitry to be used.

What is claimed is:
 1. A lead frame for assembly of a semiconductordevice within a package having a predetermined foot print, the leadframe having a plurality of leads that are formed about opposinglongitudinal sides of the package, the lead frame comprising at leastone additional lead formed within the area of the foot print of thepackage and being exposed at the bottom level of the package.
 2. Thelead frame of claim 1 wherein said at least one additional lead beingformed at one of the distal ends of the semiconductor package.
 3. Thelead frame of claim 1 comprising an additional lead formed within thearea of the footprint of the package and being exposed at the bottomlevel of the package.
 4. The lead frame of claim 3 wherein saidadditional lead being formed at the opposite distal end of thesemiconductor package.
 5. The lead frame of claim 4 wherein said atleast one additional lead and said additional lead having a generally“S” shape.
 6. The lead frame of claim 2 wherein said at least oneadditional lead having a generally “S” shape.
 7. A lead frame having aplurality of longitudinally extending opposing leads, a die bonding flagto which at least one of said opposing leads is attached, the lead framecomprising at least one additional lead formed at an end of the leadframe spatially between the opposing leads and having a generally S”shape.
 8. The lead frame of claim 7 including an additional lead formedoppositely away from said at least one lead spatially between theopposing leads and having a generally “S” shape.
 9. A thin small outlinesemiconductor package having a lead frame therein, the lead frameincluding a plurality of conductive leads extending outwardly of alongthe longitudinal sides of the semiconductor package, a die mountingportion to which a semiconductor circuit is mounted and to which one ofsaid plurality of conductive leads is connected therewith, said leadframe having at least one additional conductive lead spaced at one ofthe distal ends of the semiconductor package and having a generally “S”shape such that said lead is formed internally to the semiconductorpackage.
 10. The semiconductor package of claim 9 wherein said leadframe includes an additional conductive lead spaced at the oppositedistal from said at least one additional lead, said additional leadhaving a generally “S” shape such that said additional lead is formedinternally to the semiconductor package.
 11. The semiconductor packageof claim 10 wherein the respective bottoms of said at least oneadditional lead and said additional lead are exposed and aresubstantially level with the bottom of the semiconductor package.
 12. Alead frame for the assembly of thin small outline packages incorporatinga semiconductor circuit comprising: a first group of metallic membersincluding a die mounting portion and a first plurality of leads; a firstmetallic interconnecting tie bar in proximity of said die mountingportion for holding said first plurality of leads in alignment; a secondgroup of metallic members including a second plurality of leads alignedopposite to said first plurality of leads; a second metallicinterconnecting tie bar for holding said second plurality of leads inalignment; and at least one additional metallic lead grouped at one endof said lead frame and formed in an “S” shape extending downward fromsaid lead frame within the interior thereof.
 13. The lead frame of claim12 including an additional metallic lead grouped at the other end ofsaid lead framed and formed in a “S” shape extending downward from saidlead frame within the interior thereof.